Binders or binder systems for foundry cores and molds are known. Generally, such binders should provide cores and molds which exhibit good thermal and dimensional stability in order to result in good dimensionally accurate metal castings. In addition, such binder systems should have rapid curing times and exhibit uniform curing properties, that is, the centers of cores or molds made therefrom should be as well cured and as strong as their surfaces in order to minimize breakage or warpage.
In the foundry art, cores or molds for making metal castings are normally prepared from a mixture of an aggregate material, such as sand, and a binding amount of a binder or binder system. Typically, after the aggregate material and binder had been mixed, the resulting mixture is rammed, blown or otherwise formed to the desired shape or patterns and then cured with the use of catalysts and/or heat to a solid, cured state.
A variety of different processes for forming molds and cores have been developed in the foundry industry. One type of process known as the "hot-box" process requires that the mixture of aggregate material and binder be cured and hardened in a holding pattern or core box while subjected to heat. Another type of binder system which does not require heating in order to bring about curing or hardening, is known as a "no-bake" process.
Phenol-formaldehyde resins have been used as binders in both the "hot-box" and "no-bake" processes. Although the phenol-formaldehyde resins offer a favorable raw material cost when compared with other resins used in these processes, they have not always cured as rapidly as desired in certain applications.
The present invention is directed to the preparation of phenolic resin systems with improved curing speeds which may be used in "no-bake" or "hot-box" systems, or in other systems where a faster curing phenolic resin is desirable.